Language diversity is closely linked to a region’s climate, rather than being purely incidental, according to a new study published in the journal Nature Communications. Researchers have also found that language diversity is more heavily impacted by a region’s climate than the region’s landscape, such as altitudinal range and river density, which may contribute to isolation of cultural groups.
The research team of Xia Hua, Simon Greenhill, Marcel Cardillo, Hilde Shneemann, and LIndell Bromham from ANU in Canberra mapped languages around the world and found that areas with high year-round productivity led to more languages. The study was the first global analysis of language diversity that compares the relative importance of isolation and ecological risk.
The study first looked at the fact that the geographic distribution of the world’s approximate 7500 languages is strikingly uneven. Papua New Guinea represents over 10% of the world’s languages in <.5% of the world’s land area. Compare that to the Russian Federation, which covers 11% of the world’s land area but accounts for only 1/5% of the world’s languages.
The researchers noted that there are broad geographic patterns in the distribution of languages, notably latitudinal gradients in which diversity increases towards the equator, and languages in the tropics tend to be restricted to smaller areas than languages at higher latitudes. The hypothesis that landscape features (such as mountains and rivers) stimulate diversity by limiting human movement and dividing populations into smaller speaker groups, thus making more language diversity, was disproved, along with any direct link between biological diversity and language diversity. With that said, a general map of the locations of higher linguistic diversity does correlate with general maps of biodiversity.
The researchers tested six climatic variables for associations with language diversity: mean annual temperature, mean annual precipitation, temperature seasonality, precipitation seasonality, net primary productivity, and mean annual growing season. Among these climatic variables, precipitation seasonality and temperature seasonality has the strongest associations with language diversity.
Climate and geography are not the only factors that shape diversity, however. For example, regions of higher than expected language diversity may have had a longer period of language diversification, or have undergone a higher rate of diversification, leading to a greater accumulation of languages in these regions than in other regions of similar climate.
The overall picture supported by the analysis is that environmental factors are a significant determinant of global variation in the diversity of human languages, as they are for global variation in biodiversity. Associations between global patterns of language diversity and climate are consistent with the ecological risk hypothesis, that stable productive climates allow human cultures to persist in smaller, more localized groups.